Influence of pressure on the refractive index and relative density of glasses in the CaO-Al2O3-SiO2 system

The pressure dependences of the refractive index for aluminosilicate glasses of the compositions 0.167CaO center dot 0.167Al(2)O(3) center dot 0.666SiO(2) and 0.157CaO center dot 0.177Al(2)O(3) center dot 0.666SiO(2) at pressures up to 6.0 GPa are determined using a polarizing interference microscope and an apparatus with diamond anvils. The compressibilities of the glasses are calculated from the measured refractive indices within the framework of the theory of photoelasticity. The structural-chemical parameters NBO/T (where NBO is the number of gram-ions of nonbridging oxygen atoms and T is the total number of gram-ions of network formers) are calculated for the glasses under investigation with allowance made for the formation of triclusters and highly coordinated aluminum.